1. Technical Field
The present invention relates to a drive control signal generating circuit which generates a drive control signal for driving a motor.
2. Background Art
There exist various motors, and a type of motor in which a permanent magnet is provided on a rotor, and a phase of current supply to a plurality of coils on a side of a stator is controlled to form a rotational magnetic field and to rotate a rotor, is widely in use.
Supply of current to such a permanent magnet motor is generally executed by switching of a plurality of transistors. For example, an H-bridge structure is employed in which a pair of arms, in each of which two transistors are connected in series between a power supply and ground, are provided, and a coil is placed between intermediate points of the two arms. In this structure, an upper side transistor of a first arm and a lower side transistor of a second arm are switched ON so that a current of the first side is supplied to the coil, and an upper side transistor of the second arm and a lower side transistor of the first arm are switched ON so that a current of the second side is supplied to the coil. In this manner, the phase of the current flowing in the coil can be controlled. By providing the coils on different positions of the coil, providing the H-bridge at corresponding positions, and controlling the phase of the current supplied to the coil, it is possible to drive the motor.
Here, there is a desire to minimize the power consumption in an electronic device. In particular, the motor requires a high power at startup, but the power can be reduced after the rotation is stabilized. In order to reduce the power, PWM control is employed. However, for the PWM control, elements such as a comparator for comparing a triangular wave and a threshold value, etc., are required, and the size of the circuit is increased.